The Spaniard, who will be one of the main contenders at the Queen's grasscourt tournament and Wimbledon next month, survived a wobble in the third set and then won the tiebreak.

Rinderknech, ranked 87th, came in as a lucky loser after the withdrawal of compatriot Arthur Fils and put up a memorable fight to make the Spaniard sweat in the first-round clash.

"It was a very tough match, very difficult for me," Alcaraz said. "You know the grass is tough but I like to play here. It's a tournament that I wanted to play and it's given me a very good performance.

"I have never played a tournament except Wimbledon on grass and I wanted to play here as I couldn't play on grass at home so I came here to practice. I felt very good, but I would say I will be better in the next round," he added

Alcaraz, who slipped to world number two after suffering cramps during his semi-final defeat by Novak Djokovic at Roland Garros, will try to reclaim top spot even though he is playing in only his third career grasscourt tournament.

He will face Czech Jiri Lehecka in the second round.